Method and apparatus for depositing a magnetoresistive multilayer film

ABSTRACT

This application discloses a method and apparatus for manufacturing a magnetoresistive multilayer film having a structure where an antiferromagnetic layer, a pinned-magnetization layer, a nonmagnetic spacer layer and a free-magnetization layer are laminated on a substrate in this order. A film for the antiferromagnetic layer is deposited by sputtering as oxygen gas is added to a gas for the sputtering. A film for an extra layer interposed between the substrate and the antiferromagnetic layer is deposited by sputtering as oxygen gas is added to a gas for the sputtering. The film for the antiferromagnetic layer is deposited by sputtering as a gas mixture of argon and another gas of larger atomic number than argon is used.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of application Ser. No. 10/965,796,filed Oct. 18, 2004, the entire contents of which are incorporated byreference. This application also claims benefit of priority under 35USC119to Japanese Patent Application No. 2003-357108, filed Oct. 16, 2003,the entire contents of which are incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to manufacture of a magnetoresistive multilayerfilm utilized for such a magnetic device as giant magnetoresistive (GMR)effect element.

2. Description of the Related Art

The magnetic film technology has been significantly applied to magneticdevices such as magnetic heads and magnetic memories. For example, inmagnetic disk drive units for external storages in computers, magneticheads are mounted for read/write of information. In the field of memorydevices, magnetic random access memories (MRAM) utilizing tunnel-typemagnetoresistive films for memory elements have been developed. The MRAMare promising next-generation memory devices due to the rapidness ofread/write and non-volatility.

In magnetic devices, the magnetoresistive effect is often utilized asmeans for converting magnetic fields into electric signals. Themagnetoresistive effect is the phenomenon that electric resistance isvaried according to variation of a magnetic field in a conductor.Especially, magnetic readout heads and MRAM utilizegiant-magnetoresistive (GMR) films where the MR ratios are enormouslyhigh. “MR ratio” means magnetoresistance ratio, i.e., ratio of electricresistance variation against magnetic field variation. In the field ofmagnetic recording where further increase of recording density isdemanded for enlarging storage capacity, it is necessary to captureslight variation of a magnetic field for reading out stored information.Therefore, the GMR film technology has been utilized in many kinds ofmagnetic heads, becoming the mainstream.

FIG. 10 is a schematic 3-D view showing the structure of an example ofspin-valve type GMR films. The spin-valve type GMR film, hereinafter“SV-GMR film”, has the basic structure where an antiferromagnetic layer23, a pinned-magnetization layer 24, a nonmagnetic spacer layer(conduction layer) 25 and the free-magnetization layer 26 are laminatedin this order. In the SV-GMR film, because the pinned-magnetizationlayer 24 is adjacent to the antiferromagnetic layer 23, magnetic momentin the pinned-magnetization layer 24 is pinned to a direction by theexchange coupling with the antiferromagnetic layer 23. On other hand,because the free-magnetization layer 26 is isolated from thepinned-magnetization layer 24 by the nonmagnetic spacer layer 25,magnetic moment in the free-magnetization layer 26 is capable of freedirections in response to the external magnetic field variation.

The giant magnetoresistive effect on the SV-GMR film derives fromspin-dependant scattering of electrons on the interface. When a coupleof magnetic layers are magnetized to the same direction, free electrons,i.e., conduction electrons, are easily scattered at the interface.Contrarily, when the layers are not magnetized to the same direction,free electrons are hardly scattered at the interface. Therefore, whenthe magnetization direction in the free-magnetization layer 26 is closerto the one in the pinned-magnetization layer 24 as shown in FIG. 4, theelectric resistance would decrease. When the magnetization direction inthe free-magnetization layer 26 is closer to the opposite one to thepinned-magnetization layer 24, the electric resistance would increase.The structure performing this GMR effect is called “spin valve”, becausethe magnetization direction in the free-magnetization layer 26 is spunagainst the pinned-magnetization layer 24, which is similar to turning atap.

Tunnel-type magnetoresistive (TMR) films utilized in the MRAM have MRratios several times as much as the GMR films. The TMR films are highlyexpected for next-generation magnetic heads, because of the higher MRratios. As well as the GMR films, a TMR film has the structure where anantiferromagnetic layer, a pinned-magnetization layer, a nonmagneticspacer layer and a free-magnetization layer are laminated in this order.The nonmagnetic spacer layer in the TMR film is a very thin film made ofinsulator, through which a tunnel current flows. Resistance on thistunnel current varies depending on the relative direction of magneticmoment in the free-magnetization layer against the pinned-magnetizationlayer.

The above-described magnetoresistive multilayer films are manufacturedby laminating each thin film for each layer. Each film is deposited bysputtering or another method. In this, what is significant is that thegiant-magnetoresistive effect in GMR films and TMR films derives fromspin-dependant scattering of electrons on the interface as described.Accordingly, for obtaining a high MR ratio, what is significant iscleanness of the interface between a couple of layers. In depositing afilm for a layer on an underlying layer, if a foreign substance isincorporated in the interface or a contaminant layer is formed in theinterface, such a fault as MR ratio decrease might be brought.Accordingly, a chamber in which each film for each layer is depositedshould be evacuated at a high-vacuum pressure so that the deposition iscarried out in the clean environment. In addition, it is significant toshorten the period after the deposition for a layer until the nextdeposition for the next layer, and to maintain the clean environmentcontinuously in the period.

Interfacial flatness in magnetoresistive multilayer films is also thesignificant factor in view of enhancing the product performance.Typically, when flatness is worse on the interface of thepinned-magnetization layer and the free-magnetization layer, theinterlayer coupling would be generated, decreasing the productperformance. This point will be described in detail as follows,referring to FIG. 11.

FIG. 11 shows the mechanism of the interlayer coupling generated fromthe worsened flatness of an interface. It is assumed in FIG. 11 that themagnetization layer 24 is formed as its surface is much roughened. Thisresults in that the nonmagnetic spacer layer 25 and thefree-magnetization layer 26 are also formed with the surfaces muchroughened. If each surface of each layer 24,25,26 is completely flat,theoretically no magnetic poles would be induced in the interfaces.Contrarily, magnetic poles would be easily induced if the interfaces areroughened. For example, the magnetic lines in the angles of theroughened pinned-magnetization layer 24 generate poles at the endsbecause they terminate on the slopes of the angles. In thefree-magnetization layer 26, the magnetic lines in the roots thereofgenerate poles at the ends.

When magnetic poles are induced on the interface between thepinned-magnetization layer 24 and the free-magnetization layer 26 asdescribed, the interlayer coupling would take place between them, inspite of isolation by the nonmagnetic spacer layer 25. As a result,magnetic moment in the free-magnetization layer 26 would be captured bythe pinned-magnetization layer 24, being incapable of the free rotation.If this happens, for example, in a magnetic readout head, readoutsignals would be asymmetrical against variation of the external magneticfield (the magnetic field on a storage medium). Otherwise, response ofthe readout head would be delayed to variation of the external magneticfield. These results might cause kinds of readout errors. In a MRAM, itmight cause kinds of write-in errors and readout errors. It could alsohappen that magnetization direction in the free-magnetization layer 26does not vary against magnetization direction in thepinned-magnetization layer 24 even when the external magnetic fieldvaries. Therefore, the MR ratio tends to decrease when flatness of theinterface is worsened.

The problems of the interlayer coupling and the interfacial roughnessare discussed in J. Appl. Phys., Vol. 85, No. 8, p 4466-4468. This paperdescribes roughness is generated from the growth structure of a film. J.Appl. Phys., Vol. 7, No. 7, p 2993-2998 describes roughness of a filmwould be promoted when pressure in depositing the film is increased.After all, these papers teach that to decrease pressure in depositing afilm is effective to make the interfacial roughness small for reducingthe interlayer-coupling. However, J. Appl. Phys., Vol. 77, No. 7, p2993-2998 also points out that intermixing, which means mutualincorporation of materials through an interface, would take place whenpressure in depositing a film is decreased.

As another solution for the problem of the interlayer coupling caused bythe interfacial roughness, it is considered to thicken the nonmagneticspacer layer. However, when the nonmagnetic spacer layer is thickened inthe SV-TMR film, the flow of conductive electrons not contributing tothe GMR effect would be promoted, causing the problem of decreasing theMR ratio. The flow of those electrons is called “shunt effect”. In theTMR film, on the other hand, if the nonmagnetic spacer layer ofinsulator is thickened, the whole resistance is increased, resulting inthat the optimum tunnel current could be no longer obtained. This wouldcause the problem of decreasing the product performance.

There is still a further way to reduce roughness of an interface, whichis shown in the Japanese laid-open No. 2003-86866. In this way, afterthe film deposition for a layer is carried out, the surface of thedeposited film is treated utilizing plasma before the next filmdeposition for the next layer. However, an apparatus for this wayaccompanies the problem of scale enlargement because equipment for theplasma treatment is required. In addition, the problem of decreasing theproductivity is also accompanied because the extra step of the plasmatreatment is required.

SUMMARY OF THE INVENTION

This invention is to solve the above-described problems, and presents amethod and apparatus for manufacturing a magnetoresistive multilayerfilm having a structure where an antiferromagnetic layer, apinned-magnetization layer, a nonmagnetic spacer layer and afree-magnetization layer are laminated on a substrate in this order. Inthe method and the apparatus, a film for the antiferromagnetic layer isdeposited by sputtering as oxygen gas is added to a gas for thesputtering. Otherwise, an extra layer is interposed between thesubstrate and the antiferromagnetic layer. A film for the extra layer isdeposited by sputtering as oxygen is added to a gas for the sputtering.The film for the antiferromagnetic layer is deposited by sputtering as agas mixture of argon and another gas of larger atomic number than argonis used as the sputtering gas.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic cross-sectional view showing the structure of amagnetoresistive multilayer film manufactured by the method andapparatus as embodiments of the invention.

FIG. 2 is a schematic front cross-sectional view of a deposition chamberin the apparatus as the embodiment of the invention.

FIG. 3 schematically shows the structure of a TMR film prepared in anexperiment for confirming the effect of oxygen gas addition indepositing a film for the seed layer.

FIG. 4 shows an experimental result in relationship between volume ofadded oxygen gas in depositing the film for the seed layer and degree ofthe interlayer coupling.

FIG. 5 schematically shows an assumed mechanism of the interlayercoupling decrease by oxygen gas addition.

FIG. 6 shows an experimental result in relationship between volume ofadded oxygen gas in depositing a film for the antiferromagnetic layerand degree of the interlayer coupling.

FIG. 7 is a schematic front cross-sectional view of a deposition chamberin the apparatus as the third embodiment of the invention.

FIG. 8 shows the result of an experiment where a film for theantiferromagnetic layer was deposited using the gas mixture of argon andkrypton.

FIG. 9 schematically shows the structure of a TMR film prepared in theexperiment.

FIG. 10 is a schematic 3-D view showing the structure of an example ofthe SV-GMR films.

FIG. 11 shows the mechanism of the interlayer coupling deriving from theworsened flatness of an interface.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments of this invention will be described asfollows. First of all, structure of a magnetoresistive multilayer filmmanufactured by the method and apparatus of the embodiments isdescribed. FIG. 1 is a schematic cross-sectional view showing thestructure of the magnetoresistive multilayer film manufactured by themethod and apparatus of the embodiments. The magnetoresistive multilayerfilm shown in FIG. 1 is utilized for a magnetic head or MRAM, and worksas a SV-GMR film or TMR film. The magnetoresistive multilayer film hasthe structure where a seed layer 21, an underlying layer 22, anantiferromagnetic layer 23, a pinned-magnetization layer 24, anonmagnetic spacer layer 25, a free-magnetization layer 26 and a caplayer 27 are laminated in this order on a substrate 1.

In the magnetoresistive multilayer film, the zone formed of thepinned-magnetization layer 24, the nonmagnetic spacer layer 25 and thefree-magnetization layer 26 essentially functions as thegiant-magnetoresistive effect element. Therefore, the zone will besometimes called “functional zone” in this specification. As shown inFIG. 1, the layers 21 to 27 are laminated upward in order. This does notalways correspond to a structure in practical usage. FIG. 1 and thefollowing description are just on the assumption that a layer formed ina prior step is located lower, and a layer formed in a later step islocated upper. Therefore, if the surface of the substrate 1 is directeddownward and the layers are laminated thereon, then the underlying layer22 is located above the antiferromagnetic layer 23.

The magnetoresistive multilayer film is manufactured bysputter-deposition of each film for each layer. Therefore, themanufacturing apparatus comprises a deposition chamber. FIG. 2 is aschematic front cross-sectional view of the deposition chamber in theapparatus as the embodiment of the invention. As shown in FIG. 2, theapparatus comprises a pumping line 31 evacuating the deposition chamber3, a substrate holder 32 holding a substrate 1 at a required position inthe deposition chamber 3, a plurality of cathodes 33,34 igniting sputterdischarge in the deposition chamber 3, and sputter power sources (notshown) applying voltage for sputtering to the cathodes 33,34.

The deposition chamber 3 is the air-tight vacuum chamber comprising anopening for transferring in and out the substrate 1. This opening isopened and closed by a gate valve 30. The pumping line 31 comprises sucha vacuum pump as turbo-molecular pump, which evacuates the depositionchamber 3 through an evacuation room provided adjacent thereto. A gasintroduction line 37 is provided for the deposition chamber 3 tointroduce a gas for sputtering, hereinafter “sputtering gas”, into theinside. The gas introduction line 37 is capable of adding oxygen gas tothe sputtering gas. Concretely, argon is employed as the sputtering gas.The gas introduction line 37 comprises a pipe 371 for argon and anotherpipe 372 for oxygen. In addition to valves 374, the pipes 371,372comprise gas flow controllers 373 so that the gases can be introduced atrequired flow rates. Though argon and oxygen are mixed and introducedtogether into the process chamber 3 in this embodiment, those may beintroduced separately into the process chamber 3 and mixed therein.

The cathodes 33,34 are those for establishing the magnetron sputtering,namely magnetron cathodes. The cathodes 33,34 comprise targets 331,341and magnet units 332,342. Though detailed structure of each magnet unit332,342 is not shown in FIG. 2, a center magnet and an outer magnetsurrounding the center magnet are provided. The magnetic field by eachmagnet unit 332,343 is in the orthogonal relation with the electricfield by each cathode 33,34, establishing magnetron motion of electronsthereby. A rotation mechanism to rotate the magnet units 332,342 againstthe standing targets 331,341 may be provided for making erosions on thetargets 331,341 more uniform. Shutters 333,343 are provided in fronts ofthe targets 331,341. Each shutter 333,343 covers each target 331,341respectively when it is not used, thereby preventing it form beingcontaminated.

Though two cathodes 33,34 are shown in FIG. 2, three or more cathodesmay be provided practically. Disclosure in the Japanese laid-open No.2002-43159 can be referred to for structure and arrangement of thecathodes. The sputter power sources (not shown) are to apply negative DCvoltages or RF (radio frequency) voltages to the cathodes 33,34respectively. A controller (not shown) is provided for controlling inputpowers to the cathodes 33,34. It is preferable to control each inputpower to each cathode 33,34 independently from each other.

In this embodiment, one target 331 of one cathode 33 is made of tantalumbecause a tantalum film is deposited for the seed layer 21. Otherwise,such a material as copper or gold may be adopted for the seed layer 21.In this case, the target 331 is made of such a material. The seed layer21 has the function of controlling crystal orientations in thin filmsfor the upper layers laminated thereon.

A method for manufacturing the above-described magnetoresistivemultilayer film will be described next. As oxygen gas is added, argongas is introduced by the gas introduction line 37 at a required flowrate. In this state, when voltage is applied to the target 331 by one ofthe sputter power sources, sputter discharge is generated at the spacein front of the target 331. Through the discharge, particles sputteredout of the target 331 reach the substrate 1, thereby depositing thetantalum film for the seed layer 21 on the substrate 1. The substrateholder 32 comprises a rotation mechanism 321. The rotation mechanism 321rotates the substrate 1 against the standing target 331 so that theuniform film can be deposited. During this deposition, the other shutter343 provided for the other cathode 34 is shut to prevent the target 341from being contaminated.

In depositing another film using the other cathode 34, the other shutter343 is opened as the shutter 333 is closed. The other one of sputterpower sources is operated to carry out another sputter-deposition aswell. In this embodiment, oxygen gas is not added to argon gas indepositing other films for the layers except the seed layer 21.

The magnetoresistive multilayer film shown in FIG. 1 is manufactured bysputter-depositions of thin films for the seed layer 21, the underlyinglayer 22, the antiferromagnetic layer 23, the pinned-magnetization layer24, the nonmagnetic spacer layer 25, the free-magnetization layer 26 andthe cap layer 29 in order on the substrate 1. The thin films may bedeposited in the same deposition chamber 3 shown in FIG. 2, otherwisethose may be deposited in deferent deposition chambers. In the case thatthe thin films are deposited in the same deposition chamber 3, eachcathode and target for each film are provided therein. In this case,after the deposition under the oxygen gas addition it is preferable toevacuate the deposition chamber 3 to be at a high-vacuum pressure foreliminating residual oxygen gas prior to the next deposition. In thecase that the thin films are deposited in deferent process chambers,therebetween the substrate 1 is transferred under a vacuum pressurewithout being exposed to the atmosphere.

The point that a little of oxygen gas is added in depositing the filmfor the seed layer 21 is based on a research by the inventors forsolving the problem of the interlayer coupling. Interfacial roughnesscausing the problem of the interlayer coupling often results fromroughness of another interface located thereunder. When the surface of afilm is roughened, the surface of another film deposited thereupon isroughened as well, because the film is deposited as it traces theunderlying roughened surface. Therefore, for preventing an interfacefrom being roughened, it is significant to deposit the film locatedthereunder without roughness.

The inventors assumed that optimization of a film deposition method fora layer beneath the pinned-magnetization layer 24 would enable toflatten the interface between them. This assumedly would enable toflatten consequently the interface of the pinned-magnetization layer 24and the free-magnetization layer 26, which contributes to reduction ofthe interfacial coupling. Through the diligent research on thisassumption, it has turned out that addition of oxygen gas to thesputtering gas in depositing a film for a layer beneath thepinned-magnetization layer 24 enables reduction of the interlayercoupling. This point will be described in detail as follows.

FIG. 3 schematically shows the structure of TMR films prepared in anexperiment for confirming the effect of oxygen gas addition indepositing a film for the seed layer. Numerals in the parentheses inFIG. 3 mean thickness of the films. As shown in FIG. 3, a tantalum filmfor the seed layer 21 was deposited at 200 angstrom thickness on thethermally oxidized surface of a silicon-made substrate 1. On thetantalum film, a NiCr film for the underlying layer 22 was deposited at40 angstrom thickness. On the NiCr film, a PtMn film (Pt50Mn50 at %) forthe antiferromagnetic layer 23 was deposited at 150 angstrom thickness.On the PtMn film, for the pinned-magnetization layer 24 a couple of CoFefilms (Co90Fe10 at %) are deposited at 30 angstrom thicknessrespectively, interposing a Ru film of 30 angstrom thickness. On theCoFe films, an alumina film for the nonmagnetic spacer layer 25 wasdeposited at 9 angstrom thickness. On the alumina film, a NiFe film(Ni83Fe17 at %) for the free-magnetization layer 26 was deposited at 40angstrom thickness. On the NiFe film, a tantalum film for the cap layer29 was deposited at 50 angstrom thickness. The abbreviation “at %” means“atomic numeral ratio”. This means weight ratio converted by atomicnumber, i.e., ratio of the numbers of included atoms. For example,“Pt50Mn50 at %” means platinum of 50% atomic numeral ration andmanganese of 50% atomic numeral ratio. And, “NiCr” means materialcomponents of nickel and chromium, and does not always mean they arealloyed though often alloyed. This is the same as in other expressionsusing other combinations of the element symbols, such as “PtMn”, “CoFe”and the like.

The TMR films of the above-described structure were prepared, as oxygenpartial pressure in depositing the tantalum films for the seed layers isvaried. Then, intensity of the interlayer coupling of thepinned-magnetization layer 24 and the free-magnetization layer 26 wasmeasured in each TMR film. Argon was used as the sputtering gas, whereits partial pressure was constantly 3.2×10⁻² Pa. FIG. 4 shows theexperimental result in relationship between volume of added oxygen gasin depositing the films for the seed layers and degree of the interlayercoupling. In FIG. 4, the abscissa axis is oxygen partial pressure, andthe ordinate axis is degree of the interlayer coupling, i.e., intensityof the interlayer-coupling magnetic field (Oe), between thepinned-magnetization layer 24 and the free-magnetization layer 26.Actual data are shown in Table 1.

TABLE 1 Relationship of oxygen partial pressure in tantalum filmdeposition and degree of the interlayer coupling Oxygen partial pressureDegree of the interlayer in Ta film deposition (Pa) Coupling (Oe) 1.2 ×10⁻⁶ 9.5 1.0 × 10⁻⁵ 8.4 2.5 × 10⁻⁵ 8.4 5.0 × 10⁻⁵ 8.7

As shown in FIG. 4 and Table 1, at zero addition of oxygen gas theinterlayer coupling was about 9.7 Oe. As oxygen addition was increased,the interlayer coupling decreased. At the low oxygen partial pressure of1.2×10⁻⁶ Pa, the interlayer coupling was still the high value of 9.5 Oe.However, the oxygen partial pressure was increased at 1.0×10⁻⁵ Pa, itdecreased at 8.4 Oe. It was the same low value even when the oxygenpartial pressure was increased to 2.5×10⁻⁵ Pa. It still remained at thelow value of 8.7 Oe even when the oxygen partial pressure was increasedto 5.0×10⁻⁵ Pa. This result teaches the oxygen partial pressure ispreferably 1.0×10⁻⁵ Pa or more.

Though it has not been clear why the interlayer coupling decreases underoxygen gas addition, there might be one possibility that the film wasflattened by oxygen gas addition. This point will be described,referring to FIG. 5. FIG. 5 schematically shows the assumed mechanism ofthe interlayer coupling decrease by oxygen gas addition.

As described in J. Appl. Phys., Vol. 77, No. 7, p 2993-2998, surfaceroughness of a deposited film supposedly derives from its crystal growthstructure. Though some kinds of films are deposited in amorphous states,a magnetic film as in this embodiment is deposited in a state thatcrystals of certain largeness grow. In this, each crystal grows to becolumnar as shown in FIG. 5(1) (2). Surface roughness of the depositedfilm appears outlining the top of each columnar crystal.

When each crystal is large-size as shown in FIG. 5(1), roughness tendsto increase. When each crystal is small-size as shown in FIG. 5(2),roughness tends to decrease. On the other hand, situation where eachcrystal grows should be taken into consideration. In FIG. 5(3), it isassumed that particles 41, i.e., atoms or molecules, arrive at a surface42. Each crystal gradually grows by accumulation of the arrivingparticles 41. In this growth, the particles 41 having arrived at thesurface 42 would migrate thereon. The migrating particles 41 aresometimes incorporated into crystal grains 43 that have been formed. Byincorporation of the particles 41, the crystal grains 43 graduallyexpand. In this, if oxygen exists in the ambience, supposedly it wouldinhibit clustering in the crystal growth of the particles 41. As aresult, the crystal grains 43 are hard to expand, remaining small-size.Clustering in this means expansion of the crystal grains 43 byincorporation of the particles 41.

Though the concrete mechanism of the grain-size decrease has not beencompletely clear, it is supposed that it derives from surfaceoxidization of the crystal grains made of tantalum. Because tantalumatoms on the oxidized surface are in ionic bonds with oxygen atoms, freeelectros that should have been due to metallic bonds with other tantalumatoms would be incorporated into orbits in the oxygen atoms. As aresult, even when other tantalum atoms migrate to be nearby, they couldnot bond with the surface atoms on the crystal grains. Supposedly thisis why the crystal grains remain small-size as shown in FIG. 5(2),making the film fine-crystal-structured.

When the tantalum film for the seed layer 21 grows with such a finecrystal structure, the surface of the seed layer 21 is flattened. Thus,the underlying layer 22, the antiferromagnetic layer 23, thepinned-magnetization layer 24, the nonmagnetic spacer layer 24 and thefree-magnetization layer 26 laminated thereon would have the flattenedsurfaces as well. Therefore, the interfaces in the functional zone areflattened as well, resulting in that the interlayer coupling decreases.This is supposedly the mechanism of the described interlayer-couplingdecrease.

Anyway, the method and the apparatus of this embodiment reduces theinterlayer coupling of the pinned-magnetization layer 24 and thefree-magnetization layer 26, by adding a little of oxygen gas to thesputtering gas in depositing the film for the seed layer 21.Accordingly, there is less probability that magnetic moment in thefree-magnetization layer 26 would be captured and restricted by magneticmoment in the pinned-magnetization layer 24. This brings the merit ofreducing readout errors and response delays in a magnetic readout head,and the merit of reducing write-in errors and readout errors in a MRAM.Because this solution is not to add such an extra step as plasmatreatment, it does not accompany the problem of increasing the apparatuscost, nor accompany the problem of decreasing the productivity caused bylead-time extension for the extra step.

The following is description about the second embodiment of thisinvention. This embodiment is characterized by that oxygen gas is addedto the sputtering gas in depositing a film not for the seed layer 21 butfor the antiferromagnetic layer 23. Concretely, a deposition chamber fordepositing the film for the antiferromagnetic layer 23 comprises a gasintroduction line introducing the sputtering gas. The gas introductionline is capable of adding oxygen gas to the sputtering gas. Structure ofthe deposition chamber may be the same as of the one in the firstembodiment shown in FIG. 2, except that the target is made of the samematerial as the antiferromagnetic layer 23 to form, e.g. PtMn, InMn orthe like.

Oxygen gas addition in depositing the film for the antiferromagneticlayer 23 is also based on the result of an experiment by the inventors.FIG. 6 shows an experimental result in relationship between volume ofadded oxygen gas in the film depositing for the antiferromagnetic layerand degree of the interlayer coupling. In FIG. 6 as well, the abscissaaxis is oxygen partial pressure, and the ordinate axis is degree of theinterlayer coupling between the pinned-magnetization layer 24 and thefree-magnetization layer 26. Actual data in the result are shown inTable 2.

TABLE 2 Relationship of oxygen partial pressure in PtMn film depositionand degree of the interlayer coupling Oxygen partial pressure in Degreeof the interlayer PtMn film deposition (Pa) Coupling (Oe) 1.2 × 10⁻⁶ 9.51.0 × 10⁻⁵ 7.2 2.0 × 10⁻⁵ 7.6 3.0 × 10⁻⁵ 8.0 4.0 × 10⁻⁵ 8.2 5.0 × 10⁻⁵9.8

TMR films having the same structure as in FIG. 1 were prepared in thisexperiment. In each preparation, a PtMn film for the antiferromagneticlayer 23 was deposited at 150 angstrom thickness as well. Argon was usedfor the sputtering gas in the PtMn film deposition, as argon partialpressure was kept constantly at 0.165 Pa.

As well as the described experiment, at zero addition of oxygen gas theinterlayer coupling was about 9.7 Oe. As added oxygen gas volume wasincreased, the interlayer coupling decreased as shown in FIG. 6 andTable 2. At the low oxygen partial pressure of 1.2×10⁻⁶ Pa, theinterlayer coupling was still the high value of 9.5 Oe. However, theoxygen partial pressure was increased at 1.0×10⁻⁵ Pa, it decreased at7.2 Oe. It still remained at the low value of 7.6 to 8.0 Oe, even whenthe oxygen partial pressure was increased in 2.0×10⁻⁵ to 3.0 ×10⁻⁵ Pa.Even when the oxygen partial pressure was increased at 4.0×10⁻⁵ Pa, itwas the low value of 8.2 Oe. This result teaches the oxygen partialpressure is preferably in the range of 1.0×10⁻⁵ to 4.0×10⁻⁵ Pa.

Reduction of the interlayer coupling by oxygen gas addition in the filmdeposition for the antiferromagnetic layer 23 is considered to have thesimilar mechanism to the described one. That is, it supposedly derivesfrom the fine crystal structure of the film as a result of that surfacesof crystal grains are slightly oxidized. As understood from theabove-described result, it is also preferable, supposedly morepreferable, to add oxygen gas to the sputtering gas in both filmdepositions for the seed layer 21 and for the antiferromagnetic layer23.

Anyway, because the interlayer coupling is reduced in this embodiment aswell, it is possible to manufacture a high-quality magnetoresistivemultilayer film with much less probability that magnetic moment in thefree-magnetization layer 26 would be captured and restricted by magneticmoment in the pinned-magnetization layer 24. Therefore, it is muchpreferable for a magnetic readout head and MRAM. Moreover, itaccompanies neither increase of the apparatus cost nor decrease of theproductivity, because no extra step such as plasma treatment is added.

It is supposed that the thin-film flattening by the slight addition ofoxygen gas would function similarly in thin-film depositions for layersother than the seed layer 21 and the antiferromagnetic layer 23.Therefore, oxygen gas may be added in a thin-film deposition for anotherlayer, i.e., the underlying layer 22, the pinned-magnetization layer 24,the nonmagnetic spacer layer 25 or the free-magnetization layer 26.Still, attention should be paid for oxygen gas addition in the thin-filmdepositions for the functional zone, e.g. for the pinned-magnetizationlayer 24, because it might much affect the product property even in thecase of small volume.

As described, the thin-film flattening by small-volume oxygen gasaddition supposedly derives from free-electron incorporation throughionic bonding of atoms on crystal grain surfaces with oxygen atoms. Onthis assumption, the same effect might be brought by another gas thanoxygen, e.g. nitrogen, fluorine, chlorine, or the like. Still, attentionshould be paid as well to use of those gases, because those are muchreactive, and because those might bring a problem of erosion or propertydeterioration.

Next, the third embodiment of the invention will be described. Thisembodiment is characterized by use of the gas mixture of argon andkrypton, hereinafter “ArKr mix”, as the sputtering gas in the thin-filmdeposition for the antiferromagnetic layer 23. FIG. 7 is a schematicfront cross-sectional view of a deposition chamber in the apparatus asthe third embodiment of the invention. The deposition chamber 3 shown inFIG. 7 is for depositing a thin film for the antiferromagnetic layer 23,where one of targets is made of material of the antiferromagnetic layer23, e.g. PtMn or IrMn. As shown in FIG. 7, a gas introduction line 37provided for the deposition chamber 3 comprises a pipe 371 for argon gasand another pipe 374 for krypton gas. The pipes 371,372 comprise gasflow controllers 373 so that argon gas and krypton gas can be introducedat a required mixture ratio. Those gases may be introduced separatelyinto the deposition chamber 3 and mixed therein.

Use of ArKr mix in the thin-film deposition for the antiferromagneticlayer 23 is also based on the result of an experiment by the inventorspursuing reduction of the interlayer coupling. Assuming that thin-filmflattening for reducing the interlayer coupling is enabled by optimizingselection and flow-rate of the sputtering gas in the film deposition forthe antiferromagnetic layer 23, the inventors executed the diligentresearch. Then, prominent reduction of the interlayer coupling wasconfirmed when ArKr mix was used at the krypton mixture ratio of 10% ormore.

FIG. 8 shows the result of an experiment where films for theantiferromagnetic layers 23 were deposited using the ArKr mix. In FIG.8, the abscissa axis is the flow rate of krypton gas (SCCM), and theordinate axis is degree of the interlayer coupling between thepinned-magnetization layer 24 and the free-magnetization layer 26.Actual data in FIG. 8 are shown in Table 3. “SCCM” stands for “StandardCubic Centimeter per Minute”, which means gas flow rate per minuteconverted at 0° C. and 1 atm.

TABLE 3 Relationship of Kr flow rate in PtMn film deposition and degreeof the interlayer coupling Kr flow rate (SCCM) Interlayer Coupling (Oe)0 8.4 1.5 8.1 2 7.7 3 7.7 4 7.6 5 7.7 6 7.5 8 7.5

In this experiment, TMR films were prepared as well. Structure of thefilms is shown in FIG. 9, which has minor differences from the describedone. Numerals in the parentheses in FIG. 9 also mean thickness of thefilms. In preparing each TMR film, ArKr mix is used for the PtMn filmdeposition for the antiferromagnetic layer 23. As the total flow rate ofArKr mix was kept constantly at 20 SCCM, krypton flow rate was varied.Then, it was investigated how degree of the interlayer coupling differsdepending on the krypton flow rate. The total pressure during thedeposition was 6.0×10⁻² Pa.

As shown in FIG. 8, the interlayer coupling was the high values of 8.4to 8.1 Oe under the krypton flow rate of 0 to 1.5 SCCM. However, itdropped down to 7.7 Oe under 2 SCCM. As krypton flow rate was increasedfurther, the interlayer coupling remained at the low values of 7.7 to7.5 Oe. From this result, it has turned out that krypton flow rate ispreferably 2 SCCM or more. It means that krypton mixture ratio ispreferably 10% or more. From the result shown in FIG. 8, a higherkrypton mixture ratio, e.g. 50 to 100%, may be preferable. However, itmight bring a problem in cost because krypton is the expensive gas.

Generally, when a voltage is applied to a target for sputtering, inaddition to atoms of the target secondary electrons are released fromthe target bombarded by ions of the sputtering gas. Atoms punched outfrom the target in sputtering are called “sputter-atoms”. Some gaseousions bombarding the target are reflected or scattered without losingtheir charges, Moreover, some gaseous ions are reflected or scattered onthe target with their charges lost, becoming neutral gaseous atoms:These neutral gaseous atoms, which are hereinafter called “recoilatoms”, spring out from the target at high speeds.

When the recoil atoms strike the film being deposited on the substrate,they would be incorporated into the film to generate stress therein. Onthe other hand, the recoil atoms would function to impede clustering ofcrystals. Sputter-atoms reaching an underlying surface or the surface ofthe film being deposited would migrate thereon. The recoil atomsbombarding the surfaces would impede the migration of the sputter-atoms.

The migration impediment effect by the bombarding recoil atoms dependson the atomic number difference of the recoil atoms from thesputter-atoms. The migration impediment is more effective if atomicnumber of the bombarding recoil atoms is larger than the sputter-atoms.Contrarily, it is less effective if atomic number of the recoil atoms issmaller than the sputter-atoms.

In addition, the recoil atoms bombarding the film being deposited havethe function of re-sputtering thereon. Degree of the re-sputteringdepends on the kind of the recoil atoms, which is similar to thesputtering yield by the sputtering gas on the target. If atomic numberof the recoil atoms is larger than atoms composing the film, i.e., thanthe sputter-atoms, then degree of the re-sputtering is high.

The film having the fine crystal structure and the flattened surface issupposedly obtained by adequately balancing the migration impedimentfunction and the re-sputtering function both by the recoil atoms. Inthis, there would be a problem if the target is made of different kindsof atoms having much difference in atomic number such as Pt (atomicnumber 78) and Mn (atomic number 25), intending to deposit a film ofsuch materials. When a sputtering gas with large atomic number is used,which means atomic number of the recoil atoms is large, atoms of smalleratomic number would be punched out from the film being deposited,through the re-sputtering by the recoil atoms. As a result, thedeposited film can not be expected to have a required components ratio.

Therefore, an optimum range of the gas mixture ratio should bedetermined according to the relationship between contents of the film,i.e., materials and components ratio, and atomic number of a gas mixtureused for the deposition. In the case of PtMn film deposition using ArKrmix, it has turned out that antiferromagnetism can be obtained on thedesired components ratio of 50Pt50Mn (at %) when the krypton flow rateis 10 to 50% against argon. Because the component ratio much affects themagnetic property of a product, it is significant to determine theoptimum gas flow rates. In the case of IrMn film as well, it issignificant to control the gas mixture ratio in an optimum range toobtain the desired components ratio of the film for a high magneticproperty. From the described point of view, xenon is supposedly morepreferable to krypton if it is required to deposit a film includinganother kind of atoms with much larger atomic number.

Anyway, because reduction of the interlayer coupling is enabled in thisembodiment as well, it is possible to manufacture a high-quality TMRfilm where magnetic moment in the free-magnetization layer is notcaptured to be restricted by magnetic moment in the pinned-magnetizationlayer. Therefore, it is much preferable for a magnetic readout head andMRAM. It accompanies neither increase of the apparatus cost nor decreaseof the productivity, because no extra step such as plasma treatment isadded.

It is understood that application of the third embodiment to the firstor second embodiment would brings a more preferable result. Concretely,the gas introduction line 37 for the deposition chamber 3 shown in FIG.2 is modified so as to introduce ArKr mix as the sputtering gas, andmodified so as to add oxygen thereto. In addition to the effect of theoxygen gas addition, the effect by the mixed krypton gas is obtained inthe tantalum film deposition for the seed layer 21 or the PtMn filmdeposition for the antiferromagnetic layer 23. Therefore, the film issupposedly fattened further, reducing the interlayer coupling further.

It should be noted that a magnetoresistive multilayer film manufactureby the method or the apparatus of this invention is not limited to thedescribed SV-GMR film nor TMR film. In the structure of themagnetoresistive multilayer film manufactured by this invention, anyother layer may be interposed therebetween as far as a requiredmagnetoresistive effect is obtained. In the described embodiments, theseed layer is the example of extra layers provided between the substrateand the antiferromagnetic layer. Oxygen gas addition may be carried outin a film deposition for any other extra layer if it is provided. Thoughthis invention has the merit that no extra step is required for reducingthe interlayer coupling as described, this invention does not excludeaddition of any extra step. In this specification, such an expression as“depositing a film on a substrate” or “depositing a film on a layer”does not always mean the film is deposited as contacted on the substrateor the layer. It includes the film is deposited apart from the substrateor the layer.

1. A method for manufacturing a magnetoresistive multilayer film,comprising: laminating an antiferromagnetic layer, apinned-magnetization layer, a nonmagnetic spacer layer and afree-magnetization layer in this order on a substrate; depositing a filmfor the antiferromagnetic layer by a sputtering process as oxygen gas isadded to a gas for sputtering; and depositing films for thepinned-magnetization layer, the nonmagnetic spacer layer and thefree-magnetization layer by sputtering processes as oxygen gas is notadded to a gas for sputtering, wherein the film for theantiferromagnetic layer is made of PtMn alloy or IrMn alloy.
 2. A methodfor manufacturing a magnetoresistive multilayer film, comprising:laminating an extra layer, an antiferromagnetic layer, apinned-magnetization layer, a nonmagnetic spacer layer and afree-magnetization layer in this order on a substrate; depositing a filmfor the extra layer by a sputtering process as oxygen gas is added to agas for sputtering; depositing a film for the antiferromagnetic layer bya sputtering process as oxygen gas is added to a gas for sputtering; anddepositing films for the pinned-magnetization layer, the nonmagneticspacer layer and the free-magnetization layer by sputtering processes asoxygen gas is not added to a gas for sputtering, wherein the film forthe antiferromagnetic layer is made of PtMn alloy or IrMn alloy.
 3. Amethod for manufacturing a magnetoresistive multilayer film as claimedin claim 2, wherein: the extra layer is a seed layer; and the film forthe extra layer is made of tantalum.
 4. A method for manufacturing amagnetoresistive multilayer film as claimed in claim 1, furthercomprising: providing an extra layer between the substrate and theantiferromagnetic layer; and depositing a film for the extra layer by asputtering process as oxygen gas is added to a gas for sputtering.
 5. Amethod for manufacturing a magnetoresistive multilayer film as claimedin claim 4, wherein: the extra layer is a seed layer; and the film forthe extra layer is made of tantalum.
 6. A method for manufacturing amagnetoresistive multilayer film as claimed in claim 1, wherein: in thepinned-magnetization layer, a direction of magnetization is pinned bycoupling with the antiferromagnetic layer; and in the free-magnetizationlayer, a direction of magnetization is free.
 7. A method formanufacturing a magnetoresistive multilayer film as claimed in claim 2,wherein: in the pinned-magnetization layer, a direction of magnetizationis pinned by coupling with the antiferromagnetic layer; and in thefree-magnetization layer, a direction of magnetization is free.
 8. Amethod for manufacturing a magnetoresistive multilayer film as claimedin claim 3, wherein the seed layer controls crystal orientations inanother layer laminated thereon.
 9. A method for manufacturing amagnetoresistive multilayer film as claimed in claim 5, wherein the seedlayer controls crystal orientations in another layer laminated thereon.